IBM uses atomic microscope for direct writing

PORTLAND, Ore.  IBM on Monday (May 1) unveiled a new method of direct writing to substrates that harnesses an atomic force microscope (AFM) to electronically control molecular-scale lithography.

Similar to dip-pen lithography, the new method improves on that direct-writing technique by being electrically controlled like an inkjet printer rather than a traditional dip-pen's method of controlling writing by touching and lifting the pen to and from a substrate.

Besides nanoscale lithography for electronic circuits, IBM also predicted the method will enable even smaller nanoscale-sized microfluidic devices used for everything from DNA fingerprinting to routine blood tests. Better control and faster processing speeds enabled by IBM's discovery, the company claimed, will enable speedier electronic control of separating biological molecules for a wide variety of medical applications.

IBM measured electrophoresis speeds in the millisecond range, or 100,000 times faster than conventional electrophoresis.

For semiconductors, IBM's new electronically controlled direct writing method uses AFM positioning accuracy to define complex patterns in a variety of materials with features down to 10 nanometersfive times smaller than today's e-beam lithography equipment and 10 times smaller than photolithography. It also holds the possibility of direct writing wafers with nanoscale arrays, by using the multiple-AFM tips ganged together.

Dip-pen lithography can already harness an atomic force microscope to ink virtually any chemical compound onto a substrate with nanometer control. The AFM probe tip is dipped in an ink well containing deposition material, then is scanned across a substrate. A tiny droplet of water attached to the tip allows the molecules from the deposition material to slide off the tip and onto the substrate.

The problem with dip-pen lithography has been that the only way to control deposition was to lift and touch the pen to the substrate.

IBM said it discovered a method for controlling the deposition of materials: the ink. The trick was to modify the AFM's tip. The new tip uses the tiny cantilever connected to the cone-shaped tip to deliver molecules up or down to a substrate with 1 million volt per meter electric field. By changing the strength and duration of the field, IBM demonstrated millisecond-level control of deposition--1,000 times faster than today's best methods.

The scanning tunneling microscope was invented in the early 1980s by scientists at IBM's Zurich Research Laboratory, Gerd Binnig and Heinrich Rohrer, who were given the 1986 Nobel prize in physics
for their work. The STM needs an electrically conducting surface. Binnig overcome this limitation with his 1986 invention of the AFM, which he developed further with fellow IBM researcher Christoph Gerber and Stanford University professor Cal Quate. Scientists at IBM and elsewhere quickly modified the basic AFM design to detect such forces as magnetism, friction and electrostatic attraction. One variant, the magnetic resonance force microscope, has been perfected to the point where it can detect the the spin of subsurface single electrons.